Mpox

Introduction
Mpox, formerly known as monkeypox, is a zoonotic viral disease caused by the monkeypox virus, a double-stranded DNA virus belonging to the genus Orthopoxvirus within the family Poxviridae. It is closely related to variola virus (smallpox virus) but generally causes milder illness.

Human mpox presents as a febrile illness with a characteristic vesiculopustular rash and can be transmitted from animals to humans or between humans. Outbreaks have been documented primarily in Central and West Africa but have also occurred globally in recent years, including large multi-country outbreaks beginning in 2022.

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Virology and Classification

• Family: Poxviridae

• Genus: Orthopoxvirus

• Two main clades:

  1. Clade I (Central African/Congo Basin clade) – More severe, higher mortality rate.

  2. Clade II (West African clade) – Milder disease, lower mortality rate.

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Epidemiology

• First identified in humans in 1970 in the Democratic Republic of the Congo.

• Endemic in several African countries, with sporadic cases elsewhere linked to travel or imported animals.

• Global outbreaks in 2022–2023 affected thousands of people across multiple continents, often involving human-to-human transmission through close contact.

• Higher incidence in men who have sex with men (MSM) during recent outbreaks, likely due to transmission dynamics rather than sexual exclusivity.

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Transmission

Zoonotic Transmission

• Direct contact with infected animals (rodents, primates).

• Bites, scratches, handling meat of infected animals.

Human-to-Human Transmission

• Direct contact with lesions, body fluids, respiratory droplets.

• Prolonged face-to-face contact.

• Fomites (contaminated bedding, clothing).

• Vertical transmission (mother to fetus via placenta).

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Pathophysiology

After entry, the virus replicates at the site of inoculation, spreads to local lymph nodes, and causes primary viremia. Secondary viremia disseminates the virus to skin and mucous membranes, producing lesions. The immune response clears the virus, but severe disease can occur in immunocompromised individuals.

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Clinical Features

Incubation Period

• Typically 6–13 days (range 5–21 days).

Prodromal Phase (1–4 days before rash)

• Fever.

• Intense headache.

• Myalgia, backache.

• Lymphadenopathy (distinguishes mpox from smallpox).

• Fatigue.

Eruption Phase

• Rash progresses through macular → papular → vesicular → pustular stages, then crusts.

• Lesions often start on the face, then spread centrifugally to palms, soles, trunk, and mucous membranes.

• Lesions are deep-seated, well-circumscribed, and may be umbilicated.

• Number of lesions varies; can be localized or widespread.

Resolution

• Scabs fall off within 2–4 weeks, leaving hypopigmented scars in some cases.

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Complications

• Secondary bacterial skin infections.

• Pneumonitis.

• Encephalitis.

• Corneal infection and vision loss.

• Severe disease in children, pregnant women, and immunocompromised individuals.

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Diagnosis

Definitive Diagnosis

• PCR from lesion material (fluid or crust).

• Viral culture (specialized laboratories).

Other Tests

• Serology (IgM, IgG) – less specific due to cross-reactivity with other orthopoxviruses.

• Histopathology: Epidermal necrosis, ballooning degeneration, intracytoplasmic inclusion bodies.

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Management

General Principles

• Most cases are self-limiting.

• Supportive care is the mainstay.

• Isolation to prevent transmission until lesions have crusted and fallen off.

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Supportive Care

• Maintain hydration and nutrition.

• Antipyretics (paracetamol 500–1000 mg orally every 4–6 hours as needed; maximum 4 g/day).

• Analgesics (ibuprofen 400 mg orally every 6–8 hours as needed).

• Antihistamines for pruritus (cetirizine 10 mg once daily; chlorphenamine 4 mg every 4–6 hours).

• Wound care to prevent bacterial superinfection.

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Antiviral Therapy

Reserved for severe disease, immunocompromised patients, or those at high risk for complications.

• Tecovirimat: 600 mg orally every 12 hours for 14 days (taken within 30 minutes of a moderate/high-fat meal).

• Cidofovir: 5 mg/kg IV once weekly for 2 weeks with probenecid and hydration to prevent nephrotoxicity.

• Brincidofovir: 200 mg orally once weekly for 2 doses (monitor for liver toxicity).

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Post-Exposure Prophylaxis (PEP)

• Smallpox (vaccinia-based) vaccines provide cross-protection:

  • Modified Vaccinia Ankara (MVA-BN; Imvamune, Imvanex, Jynneos): 0.5 mL SC injection; two doses 28 days apart for unvaccinated individuals.

  • ACAM2000: Live vaccinia virus vaccine, single percutaneous dose by bifurcated needle (not preferred in immunocompromised patients).

PEP is most effective if given within 4 days of exposure; can reduce severity if given within 14 days.

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Infection Prevention and Control

• Isolation of patients until all scabs have fallen off.

• Use of personal protective equipment (PPE) for healthcare workers.

• Disinfection of contaminated surfaces and laundry.

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Prognosis

• Most patients recover in 2–4 weeks without specific treatment.

• Case fatality rates: Clade I ~10%, Clade II <1% in recent outbreaks.

• Severe outcomes more common in immunocompromised individuals.